Now here’s a topic I know quite a bit about.
First and foremost, let me nuke the idea that Hip Dysplasia (CHD) is related to “purebred” dogs.
CHD is a polygenic disease - it takes a specific combination of genes to cause it to appear. The best way to avoid picking a dog that could develop CHD is to be sure that the parents are screened by a team of radiologists like the OFA (Orthopedic Foundation for Animals), and that both parents have OFA Good or OFA Excellent hips. While these evaluations do not guarentee that your dog will not develop a degenerative joint disease like CHD, it does narrow down the chance. Generally, two OFA good parents will produce 5-10% dysplastic offspring, or less.
The major problem we face today with CHD is backyard/uninformed breeding, where a dog that looks good is bred to another dog that looks good. These dogs can have hip joints that are not good at all - and hence result in heartbreak for the families who purchased puppies…
CHD is most common in large breeds and mixed-breeds, but because for a long time people believed that little dogs didn’t get CHD, their breeds weren’t screened. This means that dogs with less-than-Good hips were bred, and thus tossed some dogs with CHD into the gene pool (not to mention backyard breeding accidents). A dysplastic dog bred to a dog with Excellent hip conformation will still produce litters of pups where 25% of them are dysplastic. Do this a couple of times, and poof… ya have a problem. So, yes, CHD in small breeds is getting worse. Good, consciencious breeders screen their animals’ hips, eyes, hearts and thyroid. For more info on the whole speil, it’s a good idea to talk to the nice folks at the ofa: http://www.offa.org
As to whether or not a smaller dog has CHD, it does occur quite a bit actually. Some breeds are more prone to developing the disorder than others - for reasons we don’t really understand. CHD is manageable - there are surgical options for treatement, such as TPO or total hip replacement. It’s awefully expensive, too. Medical management is also doable for moderate to severe cases, but is palliative.
Damnation, I should get off my soapbox, eh?
E.